In vitro effects of voxelotor on red blood cell senescence and rheological behavior in sickle cell anemia

Voxelotor, a hemoglobin S polymerization inhibitor, has been shown to reduce anemia in sickle cell anemia (SCA) but its effects on vaso-occlusive crisis frequency are limited. Its recent market withdrawal due to concerns over treatment-related excess mortality highlights the need for a better understanding of its mechanisms of action, especially with similar compounds under development. We investigated, in vitro, the effects of voxelotor on red blood cells (RBCs) from SCA patients, in hypoxia and normoxia. Parameters included: 1) RBC senescence markers including phosphatidylserine (PS) and CD47 exposure, calcium and reactive oxygen species (ROS) content measured with flow cytometry; 2) RBC aggregation assessed by light transmission; 3) RBC deformability using ektacytometry under shear stress, osmotic, and oxygen gradients. Voxelotor decreased RBC PS exposure in both hypoxia and normoxia but increased ROS levels. Voxelotor increased RBC aggregation and RBC deformability, decreased Ohyper (indicating decreased cell hydration state). The extent of RBC deformability increase with voxelotor was negatively correlated with fetal hemoglobin levels. While voxelotor demonstrated beneficial effects on RBC deformability and sickling propensity, its impact on RBC aggregation properties and ROS generation requires further investigation to better understand its different mechanisms of action.